© 2012 Armand J. Chaput
University of Texas VSP Structural
Analysis Module Update - Demonstration
VSP Workshop, San Luis Obispo, CA
Hersh Amin
Armand J. Chaput
Department of Aerospace Engineering and
Engineering Mechanics, University of Texas at Austin
7 August 2013
http://vspsam.ae.utexas.edu/
Today’s Lineup
• Overview of VSP SAM Process
• VSP Model
• Grumman A6E Intruder Wing
• VSP SAM
• Version 1
• Overview
• Tutorial:
• Shrenk’s Approximation (Air Loads)
• Load Factor: 9.75 g
• Version 2
• Overview
• Tutorial:
• Shrenk’s Approximation (Air Loads)
• Load Factor: 9.75 g
• Wing fuel
• External stores (external fuel tanks)
• Note: corresponding files can be found at:
http://vspsam.ae.utexas.edu/archieve/VSPWorkshop2013
Overview of VSP SAM Process
UT Input Executable (Java)
Boundary Conditions and Load Cases
CalculiX Input File
Vehicle Sketch Pad
External and Internal Mesh
Generation
Parametric
External Geometry
Parametric
Internal Geometry
CalculiX
FEM Solution
FEM Input
FEM Post Process
and Graphics
Output Files
UT Convergence Executable
(Java)
Solution Files
Thickness Calculation
Stress Convergence
Thickness and Material Properties
Mass Calculation
Wing Trim
VSP process through mesh generation
Vehicle Sketch Pad
External and Internal Mesh
Generation
Parametric
External Geometry
Parametric
Internal Geometry
Overview of VSP SAM Process – Vehicle Sketch Pad
UT Input Executable (Java)
Boundary Conditions and Load Cases
CalculiX Input File
Thickness and Material Properties
Wing Trim • Deletes non-primary load carrying structure
- Typically leading and trailing edge devices
• Deletes non-load carrying skin panels
- To represent typical fabric or film skin sections
Overview of VSP SAM Process – UT Input Executable
Overview of VSP SAM Process – UT Input Executable
UT Input Executable (Java)
Boundary Conditions and Load Cases
CalculiX Input File
Thickness and Material Properties
Wing Trim
Spars, Ribs and Skins can be defined as different
materials
Required Thickness
defined by input
Design Nominal
Stress (DNS)
objective and
Minimum Gauge
UT Input Executable (Java)
Boundary Conditions and Load Cases
CalculiX Input File
Thickness and Material Properties
Wing Trim
Overview of VSP SAM Process – UT Input Executable
• 2D linear load – at defined constant chord fraction
- Input based on root and tip running load
• 2D elliptical and Schrenk approximations
- Input based on flight design gross weight and nz
• Discrete point loads (Fxx, Fyy, Fzz, Mxx, Myy, Mzz)
- GUI inputs at defined % span and % chord locations
• Discrete mass loads (nz) (v2+ feature)
- GUI inputs at defined spar # and % span or rib # and % chord
locations with multiple attachment points on ribs and/or spars
• Multiple Load Cases (v2+ feature)
- GUI inputs for multiple 2D linear, elliptical or Schrenk
approximations with varying angle of attacks and varying load
distributions on spars
• Fuel Loads (v2+ feature)
- GUI inputs for adding fuel tanks between ribs and spars
- Applies pressure loads and inertial loads on the skin
Boundary conditions define which rib is fixed from
translation in the x, y and z axis
UT Input Executable (Java)
Boundary Conditions and Load Cases
CalculiX Input File
Thickness and Material Properties
Wing Trim
CalculiX
FEM Solution
FEM Input
FEM Post Process
and Graphics
Output Files
Overview of VSP SAM Process – CalculiX Solutions
Users can see status messages while VSP SAM
is running. Messages can have information on
VSP SAM’s current stress convergence iteration,
Load cases and/or Wing trim operation.
Solution
viewing
area
Mouse commands
rotate and zoom
solution
CalculiX
FEM Solution
FEM Input
FEM Post Process
and Graphics
Output Files
Left click in
white area
brings up menu
Menu provides
range of stress
& displacement
viewing options
Option shown
is von Mises
stress
Overview of VSP SAM Process – CalculiX Solutions
Simple Von Mises stress-based structural
thickness resizing algorithm developed
• An enabling capability for FEM based
structural mass property estimation
• Node thickness resizing is based on
user defined design nominal stress (DN)
or minimum gage, whichever larger
VSP SAM iterates stress to mass convergence
UT Convergence Executable
(Java)
Solution Files
Thickness Calculation
Stress Convergence
Mass Calculation
Overview of VSP SAM Process – UT Convergence Executable
Summary of theory and method used to back out required Nodal thicknesses
Background
Part of the objective of the project is to be able to determine the optimized thickness of each part of the
wing for a given working stress. This backing out the thicknesses aims to do that. The procedure used
by our team and the theory behind it is described.
Theory
We begin with an arbitrary 3D element as shown below:
The blue plane represents a plane lying in one of the 3 principal axes, showing that the element can be
arbitrarily oriented. We can then describe the stress acting on this plane as follows:
We know seek to find the required thickness for a given working stress as defined by the user:
Solving equation (1) for the force, and plugging into equation (2) it can be shown that we get:
By using the max principal stress in any given element for we can ensure that the element is sized for
the worst case scenario. This is the theory behind the procedure used.
Thickness
(1)
(2)
t’i = (/DN) ti
Build VSP Model
• Use actual Area, Taper Ratio, Dihedral, Thickness, and Span
• Model the actual Spar locations.
• Model the actual Rib locations.
Generate Mesh
• Choose mesh size depending on wing size. Typically 100 elements spanwise (Half-Span/100).
• Generate meshes.
• If mesh size > 5 Mb, increase mesh size.
Mass Convergence Minimum Gauges & DNS
• Constant Minimum Gauge
• Initial Design Nominal Stress (DNS) = Initial guess
• Vary DNS for ribs, spars and skins until final wing structure weight matches expected value.
Overview of VSP SAM Process – Mass Calibration Method
VSP Model – Why A6E Intruder ?
• Available in Metal and Composite
• Good Mass Properties
• Internal Fuel and External Stores
• Larger Operating Flight Envelope
• Good for the purpose of Software Calibration
VSP Model – A6E Planform
All locations and linear
dimensions in inches
BL
30
5
BL
31
8
33”
BL
14
4
56”
B
L 7
8
B
L 6
6
0.05 c
0.70 c
29.5
28
BL
38
.9
Sweep: 29.5
Root Chord (BL 66):
~156.53” = 13.04’
Tip Chord (BL 305):
62.125” = 5.18
NOTE: Currently VSP SAM does not
support Multi-Section Wing which
limits this analysis to intermediate
and outer sections only which will be
combined into single wing section
VSP Model – A6E Airfoil
NACA-6 Series
Airfoil
t/c (BL 66):
~0.0885 t/c (BL 305):
~0.0612
NOTE: Only Root and Tip t/c ratios
will be used since adding additional
t/c ratios need multi-section wing
which is not currently supported by
VSP SAM
All locations and linear
dimensions in inches
BL
30
5
BL
31
8
FS 228.2
FS 283.9
33”
BL
0
0.70 c?
182.6
BL
14
4
FS 0
56”
0.83 c
0.15 c
57”
318”
B
L 7
8
B
L 6
6
0.05 c
0.70 c
29.5
28
1
17”
Drawing warped L/R B
L 3
8.9
VSP Model – A6E Spars
VSP Model – A6E Ribs
Rib 0
Rib 8
9 Ribs
including Root
and Tip Rib
Spar 0
Spar 1
NOTE: To further simply the
model, all ribs are placed parallel
to free stream.
VSP Model – Modifying the new wing (A6E Planform)
2
3 6
4
1 5
Delete all sections
except section ID: 0
2
3
Set Tip Chord, Root
Chord, & Sweep
4
Set Span, &
Projected Span
6
VSP Model – Modifying the new wing (A6E Airfoil)
1
2
3
Airfoil ID: 0 1 Type:
(Dropdown
menu)
NACA
6-series
NACA
6-series
t/c ratio:
(“Thick” slider)
0.0885 0.0612
1
2
3
VSP Model – A6E FEM Geometry (Spars)
1
2
3
Spar ID: 0 1 Position:
(“Position:
Slider)
0.05 0.7
Sweep
Angle:
(“Rel”
checkbox)
Checked Checked
Relative
Sweep
Angle:
(“Sweep”
Slider)
0.00 0.00
3
VSP Model – A6E FEM Geometry (Ribs)
1
2
3
Rib ID: Position (“Position” Slider)
0 0.0
1 0.1
2 0.231
3 0.322
4 0.457
5 0.611
6 0.751
7 0.892
8 1.0
3
VSP SAM – Required Files
1
• Geom File: <Wing_Name>_calculix_geom.dat
• Thick File: <Wing_Name>_calculix_thick.dat
• Copy the “Geom File” and the “Thick File” in a separate directory to run
SAM
• NOTE: SAM working directory (next slide) must not have any spaces in its
path.
VSP SAM – Import VSP Mesh
1 2 3 Set directory for VSP Mesh Files.
You can choose either
calculix_geom or calculix_thick file.
NOTE: having spaces in the
directory path will result in crash.
1
Set the directory of the CalculiX
folder
(use default with typical installation)
2
Open GUI inputs from previous
session or Save GUI inputs for
future sessions
3
1
2
3 Open
3 Save
VSP SAM – Sign Conventions
Y
Z
X X axis goes
chordwise
Y axis goes
spanwise
Z axis goes
normal to the
Datum
α
Origin is always at wing Apex
and parallel to the VSP
coordinate system.
Datum
Applies to all the load factors including nx, ny, and nz
NOTE: All Axis are parallel or
perpendicular to the Datum
regardless of wing sweep,
dihedral or angle of attack
Y axis
goes into
the page
VSP SAM – Version 1
Features:
• Skin Trim Feature
• Load Spar Approximations
• Boundary Condition
• Separate FEM Models
• Special Case: “Zero” Node Thickness
• Stress Convergence and Node Sizing
• Mass Calculation
VSP SAM – Skin Trim Feature
Remove non-load carrying skin
panels which can be fabric
sections of the skin, landing
gear hatches, etc.
Skin trim must be defined by
Inboard/Outboard rib and
Forward/Aft spar
VSP SAM – Load Spar Approximations
Planform Shape, Elliptical and Schrenk’s Approximations:
Schrenk’s Load distribution is equivalent to average of elliptical load distribution
and the actual planform shape distribution of the wing.
VSP SAM – Boundary Condition
Rib 0 is fixed from
translation in the x,y and
z axis as shown in the
CalculiX results file.
As a result, this particular
wing structure is a
cantilever beam with Rib
0 as the stationary plane.
Any Rib can be defined
as a fixed rib such as a
“Body Rib” as shown in
the figure below.
Rib 0 Body Rib
VSP SAM – Separate FEM Models
Version 0 contains Single FEM model results from original VSP’s output files
Version 1 Splits FEM into separate Skin, Rib, and Spar FEM models using “Rigid
Body Elements” to make connections at rib-skin, spar-skin, and rib-spar intersections
When node thickness is
resized to meet user defined
DNS objective, different node
thickness requirements at
intersections distort elements
which results in CalculiX error
Thicker
elements at rib-
skin, spar-skin,
and rib-spar
intersections
VSP SAM – Special Case: “Zero” Node Thickness
y
z
Set of vertical nodes from a spar, with the horizontal lines representing the
thickness of each node and the Red Arrow represents the force applied to this set
Before After
Thickness of
some nodes
approaches at
nearly zero after
convergence Solution: Apply average
thickness of the adjacent
nodes to the affected node
NOTE: Set of nodes from a
spar is only used as an
example, The same method
applies to any affected node
within the FEM model
VSP SAM – Stress Convergence and Node Sizing Summary of theory and method used to back out required Nodal thicknesses
Background
Part of the objective of the project is to be able to determine the optimized thickness of each part of the
wing for a given working stress. This backing out the thicknesses aims to do that. The procedure used
by our team and the theory behind it is described.
Theory
We begin with an arbitrary 3D element as shown below:
The blue plane represents a plane lying in one of the 3 principal axes, showing that the element can be
arbitrarily oriented. We can then describe the stress acting on this plane as follows:
We know seek to find the required thickness for a given working stress as defined by the user:
Solving equation (1) for the force, and plugging into equation (2) it can be shown that we get:
By using the max principal stress in any given element for we can ensure that the element is sized for
the worst case scenario. This is the theory behind the procedure used.
Thickness
(1)
(2)
t’i = (/DNS) ti
1 and Thickness1 corresponds to each node
VSP SAM (version 1) – A6E Wing Geometry
1 2
3
2
Initial Thickness definitions
Set boundary conditions
(Fixed Rib) which indicates
which Rib is fixed from
translation in x, y, and z
direction and Convergence
Tolerance which ends the
iterative process when the
mass difference between
previous iteration and
current iteration converges
to the user defined
tolerance
3
VSP SAM (version 1) – A6E Wing Trim (cont’d)
Leading Edge Trim Trailing Edge Trim
1 1 2 2
3 3
4 4
Device Trim definition to reveal the Wing Box of the A6E Intruder Wing
VSP SAM (version 1) – A6E Material Properties
1 2
3
Set Material Properties such as
Young’s Modulus, Poisson’s
Ratio, Yield Stress and Ultimate
Stress
Assign materials defined (2) to
each component and set the
Design Nominal Stress (DNS)
as well as Density and Minimum
Gauge (minimum thickness) for
each component
3
For this case, properties of 2024 T3
Aluminum Alloy is used which is a
nominal material for metal wings,
and Minimum gauge of typical
military aircraft wing is used.
MIL-HDBK-5, Table 3.2.3.0(d)
NOTE: Throughout VSP
SAM, ft and lbm will be the
nominal units.
VSP SAM (version 1) – A6E Aircraft Weight
Wing External Loads (distributed)
0
2000
4000
6000
8000
10000
12000
0.000 0.100 0.200 0.300 0.400 0.500
y/b
lbf/
ft
Running Load pFuel inertia relief
Wing External Load Fraction
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0.00 0.10 0.20 0.30 0.40 0.50
y/b
Lo
ad
fra
cti
on
External loadInertia relief
Load Fraction at BL66 (root):
0.73 of Flight DGW
26664 lbm
NOTE: Only 73 % of the
Flight DGW will be used
since this analysis only
involves the intermediate
and outer sections of the
A6E Wing
Flight Design Gross
Weight (DGW):
36526 lbm
VSP SAM (version 1) – A6E Load Case
1
http://hyperphysics.phy-astr.gsu.edu/hbase/fluids/airfoil.html
2
3
4
NOTE: All of the Aircraft
Load will be placed on
Spar 0 Only due to VSP
SAM version 1 limitation
VSP SAM – Viewing CalculiX Results
1
NOTE:
These files can be
found in the same
directory where VSP
Mesh files are located
In version 2, “Wing1_N” represents
CalculiX results for Case ID 1 set
in “Load Case” tab at iteration N.
Highest “N” represents the final
iteration.
NOTE: In version 1, “Wing1” from “WingN” is used where “N”
represents the iteration number. “Wing_initial” represents the
initial iteration and “Wing_final” represents the final iteration.
VSP SAM – Viewing CalculiX Results (cont’d)
2 1
3
Translate Model:
Use Right Mouse
Button
Rotate Model:
Use Left Mouse
Button
Zoom in/out Model:
Hold scroll wheel
while dragging the
mouse
VSP SAM – Mass Results File
NOTE:
These files can be
found in the same
directory where VSP
Mesh files are located
“mass.csv” consists of mass values of each
component as well as volume and surface
area at each iteration.
NOTE: VSP SAM only outputs the mass
values in “mass.csv” file. It does not plot any
values as of right now.
VSP SAM (version 1) – A6E Stress Results (Iteration 0)
DNS
Skin: 46.181 ksi
Spars: 16.875 ksi
Ribs: 12.361 ksi
VSP SAM (version 1) – A6E Stress Results (Iteration 7)
DNS
Skin: 46.181 ksi
Spars: 16.875 ksi
Ribs: 12.361 ksi
VSP SAM – Version 2
Features:
• Multiple Load Spars & Angle of Attack
• Multiple Load Cases
• Wing Fuel Loads
• Discrete Mass Loads
VSP SAM – Multiple Load Spars & Angle of Attack
http://www.pilotfriend.com/training/flight_training/aero/pres_pat.htm
α > 0
α = 0
Red Arrow
represents
the resultant
force applied
on the wing
x
z
• Based on Angle of Attack (α), loads are split in x and z directions.
• Each spar can be assigned a load fraction of the Total Load in order to get
the resultant force applied on the wing.
VSP SAM – Multiple Load Cases
• More than one Load case can be assigned with varying Angles of Attack
and varying Load Spar Distributions.
• Constructs new FEM model from using Max Stress on each node and Max
Thickness of each node out of all the user-defined load cases.
• The new FEM model is used to calculate final mass estimate.
1 2
3 4
Positive High Alpha
1
Positive Low Alpha
2
Negative Low Alpha
Negative High Alpha
3
4
All 4 points of the flight envelope
can be analyzed
VSP SAM – Discrete Mass Loads
• Adds inertial loads on the spars and/or ribs with multiple attachment points.
• User defines spanwise/chordwise fraction along with spar/rib numbers and load fraction of the Total Load for a given attachment point.
• Adds load along the neutral axis of the rib or spar (figure 2). • Distributes loads based on the distance from user-defined spar/rib
location (figure 1).
Node 1 Node 2
Location
D1 D2
Loads are applied in the nz direction
figure 1
figure 2
VSP SAM (version 2) – A6E Initial Inputs
1
Same inputs as version 1:
Wing Trim (Devices Tab)
Wing Geometry
1
VSP SAM (version 2) – A6E Material Properties
2
3
Same inputs as version 1
Different DNS for each
component. Same Minimum
Gauge and Density as version 1
1
VSP SAM (version 2) – A6E Load Case
1 2
3
4
5
6
7
Load
Parameters: 0 1
Spar #: 0 1
% of Load: 0.75 0.25
Fixed End
Moment:
0.0 0.0
4
http://hyperphysics.phy-astr.gsu.edu/hbase/fluids/airfoil.html
VSP SAM (version 2) – A6E Wing Fuel Tanks
Fuel Tanks
78. Starboard Wing
Integral Fuel Tank
91. Outer Panel
Integral Fuel Tank
84. Outer Wing
Missile Pylon
201. Inboard Wing
Pylon
Top View
VSP SAM (version 2) – A6E External Stores
y
z
Rib 0 Rib 8
Rear View
y
x
Spar 0
Spar 1
Rib 1 Rib 4
Attachment
Points
Inboard Fuel Tank Outboard Fuel Tank
Pylon
Tank w/adapter External Stores: Inboard: Outboard:
Pylon (lbm): 96.3 91.7
Tank w/adapter (lbm): 199 199
Fuel (lbm): 2005 2005
Total Mass (lbm): 2300.3 2295.7
VSP SAM (version 2) – Adding A6E External Stores
1 2
3
4
5
6
Mass ID: 0 1
Mass(lbm): 2300.3 2295.7
Load Factor
(nz):
-9.75 -9.75
Rib #: 1 4
Chordwise
Fraction:
0.5 0.5
3
4
Note: All masses are
attached at ribs
4
VSP SAM (version 2) – Adding A6E Wing Fuel
1 2
3
4
5
Tank
ID:
Inboard
Rib
Outboard
Rib
FWD
Spar
Aft
Spar
0 0 1 0 1
1 1 2 0 1
2 4 5 0 1
3 5 6 0 1
4 6 7 0 1
5 7 8 0 1
4
VSP SAM (version 2) – A6E Stress Results (Iteration 0)
DNS
Skin: 42.569 ksi
Spars: 15.069 ksi
Ribs: 9.028 ksi
VSP SAM (version 2) – A6E Stress Results (Iteration 6)
DNS
Skin: 42.569 ksi
Spars: 15.069 ksi
Ribs: 9.028 ksi
Top Related